Munro's selection of books is vastly superior to Indigo's, but I do think that Bolen Books could do a better job in terms of adding inventory. Their shelves could easily handle twice as many titles as they currently do because most of the shelves are stocked with 'turn outs' with the cover fully exposed, as opposed to being shelved 'spine-out' (i.e the 'normal' way). The book business essentially works on the consignment model whereby the retailer doesn't pay the publisher for inventory until a book is sold (the retailer will typically get to keep 40-45% of the cover price of each book) and any unsold inventory is simply returned to the publisher to be 'remaindered' as bargain books. Thus, it wouldn't 'cost' Bolen to much to increase inventory: they would just have to deal with more returns and perhaps a marginal bit of extra overhead.
If I discover a book that I might want to purchase I usually check the websites of Munro's, Bolen Books, and Indigo to see which store has it in stock. Aside from bestsellers, Munro's is often the only one of the three to have the book in stock. While I've sometimes ordered books online, I find that I often want to flip through a book in-hand before deciding whether or not to purchase it, and (aside from bestsellers) both amazon.ca and Indigo offer minimal discounts (less than 10%) on many titles when ordering online.